1. Field of the Invention
The invention relates to high gas barrier, delamination-resistant polyamide compositions suitable for extended shelf-life packaging applications. The invention also pertains to polyamide compositions exhibiting high oxygen scavenging capability. The polyamide products are particularly suited for producing barrier packaging articles such as monolayer or multi-layer films, sheets, thermoformed containers and molded bottles. Such articles are useful in a variety of oxygen-sensitive food, beverage, pharmaceutical, and health care product packaging applications.
2. Description of the Related Art
It is well known in the art to polyamide based packaging articles such as films, bottles and containers, which are useful for food packaging. In order to enhance freshness preservation, it is well known to package food and beverage products within a packaging structure composed of multiple layers of two or more different plastics. For example, U.S. Pat. Nos. 5,055,355 and 5,547,765 teach laminates of polyamides and ethylene vinyl alcohol copolymers which have good oxygen barrier properties. Such packaging structures generally include a barrier plastic layer which has low permeation to oxygen and/or carbon dioxide.
In order to enhance freshness preservation, it is standard practice to package food and other materials within a laminated packaging material that generally includes a barrier layer having a low permeability to oxygen. The material can be thin, allowing it to be wrapped around the material being packaged, or it can be sufficiently thick to form a shaped container body. It is further known to include an oxygen scavenger in polymeric packaging materials. The oxygen scavenger reacts with oxygen that is trapped in the package or that permeates into the package. This is described, for instance, in U.S. Pat. Nos. 4,536,409 and 6,423,776.
Various types of oxygen scavengers have been proposed for this purpose. U.S. Pat. No. 4,536,409 recommends potassium sulfite as an oxygen scavenger. U.S. Pat. No. 5,211,875 discloses, the use of unsaturated hydrocarbons as oxygen scavengers in packaging films. It is also known in the art that ascorbic acid derivatives as well as sulfites, bisulfites, and phenolics, can be oxidized by molecular oxygen, and can thus serve as an oxygen scavenging material. U.S. Pat. Nos. 5,202,052 and 5,364,555 describe polymeric material carriers containing oxygen scavenging material. These polymeric carriers for the oxygen scavenging material include polyolefin, PVC, polyurethanes, EVA and PET.
There is an ongoing need in the art for a high barrier polymeric material which can provide low permeation of gaseous permeates through the material, as well as high oxygen scavenging capability. The present invention provides new polymeric compositions and structures formed therefrom that show such excellent gas barrier performance as well as high oxygen scavenging capacity, resulting in extended shelf lives of packaged foods or beverages.
More particularly, polymeric compositions of the invention are slow crystallizing blends including a first polyamide comprising a crystallizable polyamide homopolymer, copolymer or polyamide nanocomposite, or a blend thereof, and a second polyamide comprising a m-xylylene diamine moiety, an isophthalic acid moiety and at least one additional moiety comprising a polyamide monomeric precursor. Also provided are direct blends of the above polyamide compositions with other polymeric materials, for example, polyethylene terephthalate (PET), and articles formed therefrom. Each of the above compositions show good melt processability, good miscibility and slow crystallization to give a barrier layer with a high clarity and good adhesion to other polymer layers in multilayer structures. The compositions also exhibit good recyclability. The composition can also be used for applications of gas barrier films requiring oxygen scavenging capabilities.